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Hardware interview practice

Increment a four-digit BCD counter

MediumRTL DesignSystemVerilog

Accept four valid binary-coded decimal (BCD) digits, add one without converting the packed value to binary, and return a stallable ready/valid response. Wrap 9999 to 0000 and flag the wrap.

Reviewed example

Work through one case

Input
accepted BCD values 1999, then 9999; stall the second response
Expected output
1999 -> 2000 carry_out=0; 9999 -> 0000 carry_out=1, held stable while stalled

Decimal carry propagates across trailing nines, and the all-nine case wraps all four digits with one carry flag.

What to cover

Requirements

  1. Treat each input digit as a decimal value from 0 through 9.
  2. Propagate decimal carry across any run of trailing nines.
  3. Create exactly one output transaction for every accepted input transaction.
  4. Hold all result digits and carry_out stable while out_valid is asserted and out_ready is low.
Continue practicing
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